Submersible lights for swimming pools are known, and generally comprise a sealed light unit behind a removable glass window and recessed into the wall of the pool. For maintenance, the water level is lowered, the glass window unbolted or unscrewed, and the lamp replaced. The lamp itself is conventionally a tungsten filament lamp, a fluorescent discharge tube or even a quartz halogen lamp. The technology is very basic and unsophisticated. US-A-2003/0048632 discloses a swimming pool light that uses diodes as the source of illumination.
Underwater hull light units for marine use are much more demanding. Generally, the illumination required is far brighter than a tungsten filament lamp bulb or fluorescent discharge tube could generate. Quartz halogen or metal halide HQI lamps are therefore used. The lamp is mounted internally of the marine vessel, and the light is directed outwardly through a window in the back of a cofferdam in the hull. A cofferdam is a recessed portion of the hull. In the case of a metal-hulled vessel the cofferdam is typically created by cutting a hole in the hull and welding in place a truncated metal cylinder. The line of truncation is flush with the outer surface of the hull. The back of the recess so created is typically vertical and includes the window through which the light shines. In the case of a fibre-reinforced hull the cofferdam is normally moulded integrally with the hull.
For marine insurance purposes the cofferdam installation for an underwater hull lighting unit must be as reliable as the remainder of the hull. It is in fact tested as if it were an integral part of the hull. For that reason it has never before been thought feasible to wire the submersible lights through the wall of the cofferdam to the interior of the cofferdam. Almost always the wiring and the light source has been internally of the hull, and the light generated has been passed through the window in the cofferdam back wall. The only alternative method of mounting that has been used is to provide a sealed window across the front of the cofferdam, with the lighting unit housed inside a dry interior of the cofferdam and wired through the cofferdam wall to the hull interior. That has been feasible only because the cofferdam wall has been isolated from the surrounding water by the sealed front window.
The development of high output light emitting diodes (LEDs) of at least one watt per LED, more recently at least three watts per LED, has created a new and exciting opportunity for developing even brighter underwater lighting units. Modern high output LEDs have a very long mean lamp lifetime and can therefore be regarded as being substantially maintenance-free. They do, however, have a relatively high heat output from the rear of the LED and are therefore generally incorporated into relatively expensive cooling enclosures which obtain their cooling by complex heat sinks or by oil cooling.
Moreover the intensity of the illumination can be vastly increased by the use of individual collimators, one associated with each LED, to direct or focus the light output of the LEDs. The use of an array of even 1 watt LEDs, the least powerful of this new range of LEDs, in conjunction with collimators for the individual LEDs will produce a light output so bright that one would not wish to look directly at the light source. US-A-2003/0048632 does not contemplate the use of collimators, which in any case would be directly opposed to the general teaching of that Patent specification which even contemplates forming the LED clusters in the shape of letters in order to ‘personalize’ an illuminated swimming pool.
What is needed is a robust and reliable underwater light unit utilising modern high power LEDs in a novel enclosure which, instead of isolating the light source from the surrounding water, takes maximum benefit from the cooling potential of the surrounding water and brings the LEDs and the surrounding water into close heat-exchange relationship.